A student investigated the temperature change when different masses of iron powder were added to 100 cm3100\text{ cm}^3100 cm3 of copper(II) sulfate solution. The results are shown in the table below:
| Mass of iron in g\text{g}g | Temperature rise in °C\text{°C}°C |
|---|---|
| 0.60.60.6 | 1.81.81.8 |
| 1.21.21.2 | 3.63.63.6 |
| 1.81.81.8 | 5.45.45.4 |
| 2.42.42.4 | 6.36.36.3 |
| 3.03.03.0 | 6.36.36.3 |
The student plots these results on a graph of temperature rise against mass of iron. They draw a straight line of best fit through the first three points (starting at the origin) and another straight horizontal line through the last two points.
Determine the mass of iron at the point where these two lines intersect.
Suggest why the temperature rise remains constant at 6.3 ∘C6.3\text{ }^{\circ}\text{C}6.3 ∘C for masses of iron of 2.4 g2.4\text{ g}2.4 g and above.
State and explain the effect on the initial temperature rises (for masses below the intersection point) if the experiment were repeated using the same masses of zinc powder instead of iron powder. Do not refer to the difference in reactivity of the two metals. [Relative atomic masses: Fe=56\text{Fe} = 56Fe=56, Zn=65\text{Zn} = 65Zn=65]
